The present invention relates to the field of low cost, flexible pressure vessels, particularly containment envelopes having inner bladders therein.
U.S. Pat. No. 5,509,255 discloses a low cost, flexible pressure vessel which comprises a flexible, air permeable containment envelope having an interior cavity and an access opening closed by a closure and a flexible, air tight, liquid impervious inner bladder having an interior cavity and an access opening closed by a closure, the inner bladder being disposed within the interior cavity of the containment envelope. The inner bladder in a fully expanded condition is larger than the containment envelope such that internal pressure acts upon the inner bladder to place the inner bladder in compression within the interior cavity of the containment envelope while placing the containment envelope in tension. The containment envelope is preferably a spunbonded olefin material available from E. I. DuPont de Nemours and Company, Inc., Wilmington, Del. (hereinafter xe2x80x9cDuPontxe2x80x9d), under the registered trademark Tyvek(copyright). The inner bag may be a readily sealable polymer bag. The pressure vessel is well suited for transporting hazardous materials therewithin by air transport. Hazardous material within a container, e.g., a vial, bottle, petri dish or blood bag, is placed inside the inner bladder, so that if any hazardous material leaks from the container it will not escape the liquid impervious inner bladder.
The closure on the containment envelope of the pressure vessel is typically in the form of a flap which is held closed by means of a strip of hot melt adhesive which has been applied to the envelope during its manufacture.
A problem with the above described pressure vessel is that under the levels of pressure that the vessels are typically exposed to in use, the vessels have a tendency to burst open. Specifically, the closures, or flaps, of the containment envelopes have a tendency to open by creep failure. The failure begins as a pucker in the center of the closure which grows over time until the closure opens completely. Once the closure opens, the internal pressure in the inner bladder acts directly on the inner bladder itself causing the inner bladder to burst, as the inner bladder is a polymer bag of low strength.
An object of this invention is to provide an improved pressure vessel that will not open at pressures typically encountered at high altitudes.
An additional problem with the above described pressure vessel is that it is possible for someone to tamper with the contents of the pressure vessel once it is sealed such that it can not be detected by visual inspection. This may be accomplished by steaming open the closure of the containment envelope, tampering with the contents thereof, then applying additional adhesive to the closure flap and resealing the closure.
An object of the invention is to provide a pressure vessel that will indicate whether or not it has been tampered with after being sealed.
The present invention provides an improved pressure vessel, comprising:
a flexible, air permeable, liquid permeable, containment envelope having an interior cavity and an access opening closed by a closure and forming a seam;
a separate, flexible, air tight, liquid impervious, inner bladder having an interior cavity and an access opening, the inner bladder being disposed within the interior cavity of the containment envelope in an unexpanded state, wherein the inner bladder in a fully expanded condition outside of the containment envelope is larger than the interior cavity of the containment envelope; and
a seal comprising a piece of flexible sheet material adhered to the exterior of the containment envelope over the seam.